Dual mode test access port method and apparatus

ABSTRACT

Two common varieties of test interfaces exist for ICs and/or cores, the IEEE 1149.1 Test Access Port (TAP) interface and internal scan test ports. The TAP serves as a serial communication port for accessing a variety of circuitry including; IEEE 1149.1 boundary scan circuitry, built in self test circuitry, internal scan circuitry, IEEE 1149.4 mixed signal test circuitry, IEEE P5001 in-circuit emulation/debug circuitry, and IEEE P1532 in-system programming circuitry. Internal scan test ports serve as a serial communication port for primarily accessing internal scan circuitry within ICs and cores. Today, the TAP and internal scan test ports are typically viewed as being separate test interfaces, each utilizing different IC pins and/or core terminals. The need for different IC pins and/or core terminals is overcome by an interface in accordance with the disclosure that allows the TAP and internal scan test ports to be merged so they both can co-exist and operate from the same set of IC pins and/or core terminals. Further, this interface allows merged TAP and scan test port interfaces to be selected individually or in groups.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/697,150,filed Apr. 5, 2007, currently pending;

Which was a divisional of application Ser. No. 11/273,754, filed Nov.15, 2005, now U.S. Pat. No. 7,219,283, issued May 15, 2007;Which was a divisional of application Ser. No. 09/845,879, filed Apr.30, 2001, now U.S. Pat. No. 7,003,707, issued Feb. 21, 2006;which claims priority under 35 USC 119(e)(1) of provisional applicationSer. No. 60/212,417, filed Jun. 19, 2000 and provisional applicationSer. No. 60/200,418 filed Apr. 28, 2000.

This application is related to provisional application Ser. No.60/207,691, filed May 26, 2000, now U.S. Pat. No. 7,058,862, issued Jun.6, 2006, which is hereby incorporated by reference, and application Ser.No. 09/845,562, filed Apr. 30, 2001, now abandoned.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to integrated circuits and,more particularly, to test interfaces exist for integrated circuitsand/or cores

BACKGROUND OF THE DISCLOSURE

FIGS. 1A-G illustrate the test architecture of a conventional 1149.1TAP. The TAP includes a TAP controller, instruction register, and set ofdata registers. The set of data registers includes; (1) an internal scanregister, (2) an in-circuit emulation (ICE) register, (3) an in-systemprogramming (ISP) register, (4) a boundary scan register, and (5) abypass register. Of the data registers, the boundary scan register andbypass register are defined by the IEEE 1149.1 standard. The other showndata registers are not defined by 1149.1, but can exist as optional dataregisters within the data register section of the 1149.1 standardarchitecture. The TAP controller responds to a protocol input on the TCKand TMS inputs to coordinate serial communication through either theinstruction register from TDI 101 to TDO 102, or through a selected oneof the data registers from TDI to TDO. The TRST input is used toinitialize the TAP to a known state. The operation of the TAP is wellknown.

FIG. 1B illustrates an IC or intellectual property core circuitincorporating the TAP and its TDI, TDO, TMS, TCK, and TRST interface. Acore circuit is a complete circuit function that is embedded within anIC, such as a DSP or CPU. FIGS. 1C-1G illustrate the association betweeneach of the data registers of FIG. 1A and the target circuit theyconnect to. The data registers are commonly connected at their serialinput to TDI 101. The data registers are separately connected at theirrespective serial outputs 104-108 to associated inputs of multiplexer103, so that they can be individually selected by an instruction tooutput data on TDO 102 during a data register scan.

FIG. 2 illustrates the state diagram of the TAP controller of FIG. 1A.The TAP controller is clocked by the TCK input and transitions throughthe states of FIG. 2 in response to the TMS input. As seen in FIG. 2,the TAP controller state diagram consists of four key state operations,(1) a Reset/RunTest Idle state operation where the TAP controller goesto either enter a reset state, a run test state, or an idle state, (2) aData or Instruction Scan Select state operation the TAP controller maytransition through to select a data register (DR) or instructionregister (IR) scan operation, or return to the reset state, (3) a DataRegister Scan Protocol state operation where the TAP controller goeswhen it communicates to a selected data register, and (4) an InstructionRegister Scan Protocol state operation where the TAP controller goeswhen it communicates to the instruction register. The operation of theTAP controller is well known.

FIG. 3A illustrates a conventional internal scan test port interface toan internal scan register. The scan test port includes a scan input(SI), scan output (SO), scan enable (SE), capture select (CS), and clock(CK) inputs. The CK input may be the circuits functional clock or it maybe a dedicated test clock input. The SE input is used to place thecircuit in a scan test mode. Placing the circuit in a scan test mode mayinvolve conditioning a circuit input for providing the SI input,conditioning a circuit output for providing the SO output, andconditioning a circuit input for the CS input, as indicated by thedashed circles. The SE input may also be used to condition the scanregister and logic circuitry such that it operates in a safe mode duringthe test. For example, it may condition the logic circuit such that nocontention occurs between logic outputs during the scan test. In testmode, SI provides the serial input to the internal scan register, SOprovides the serial output from the internal scan register, CS providesthe control input protocol to cause the internal scan register tocapture response data from the logic circuitry then shift data throughthe scan register from SI to SO to unload the captured response data andload the next stimulus data to be applied to the logic circuitry.

FIG. 3B illustrates an IC or core incorporating the scan test port (STP)of FIG. 3A. For ICs, the SI, SO, and CS signals are typically sharedwith functional signal pins to save pin count while the SE signal istypically a dedicated IC pin so that it can be accessed to switch theshared pins between their functional and SI, SO, CS test modes. The CKsignal may be the ICs functional clock or it may be a dedicated testclock. For cores, the SE, SI, SO, CS, and CK signals may all bededicated for scan test access since cores typically do not suffer fromthe pin count problem that ICs do. The role of the SE signal on coresmay only be to condition the scan register and logic circuitry for thepreviously mentioned safe operation during the test, instead of beingused to switch inputs and outputs between functional and test mode asmentioned for the IC scan test port SI, SO, and CS signals.

FIG. 3C illustrates an IC or core including both the STP of FIG. 3A andthe TAP of FIG. 1A. In FIG. 3C it is seen that the TAP and the STPrequire different interface signals since their input and outputoperations are based on different serial interface protocols.

FIG. 4 illustrates a system IC consisting of cores 1-N. Each coreincludes a TAP interface and a STP interface. The core TAPs are seriallyconnected, via a first scan path wiring bus 410, to allow a tester toaccess the TAPs of embedded circuits in the cores, such as the embeddedtarget circuits of FIGS. 1C-1F. The STPs are serially connected, via asecond scan path wiring bus 420, to allow a tester to access the STPs ofembedded internal scan circuitry of the cores, such as the scancircuitry of FIG. 3A. From FIG. 4 it is seen that the system IC requirestwo test interfaces, one for the core TAPs and another for the coreSTPs. Further, the IC requires two separate internal scan path wiringbuses one scan path wiring bus 410 for the core TAPs and another scanpath wiring bus 420 for the core STPs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1G illustrate the test architecture of a conventional 1149.1TAP.

FIG. 2 illustrates the state diagram of the TAP controller of FIG. 1A.

FIG. 3A illustrates a conventional internal scan test port interface toan internal scan register.

FIG. 3B illustrates an IC or core incorporating the scan test port (STP)of FIG. 3A.

FIG. 3C illustrates an IC or core including both the STP of FIG. 3A andthe TAP of FIG. 1A.

FIG. 4 illustrates a system IC consisting of cores 1-N.

FIG. 5A illustrates the structure of the present disclosure to utilize asingle IC test interface and a single internal scan path wiring bus toprovide access to the internal scan circuit 501 from either the TAP orSTP of FIG. 4.

FIG. 5B illustrates an individual scan cell used in FIG. 5A.

FIGS. 5C and 5D illustrate multiplexers used in FIG. 5A.

FIG. 6 is an embodiment of the present disclosure illustrating that thesource of the Lock Out signal could come from an additional IC pin orcore terminal, or from a register (R) or other circuit embedded withinthe system IC.

FIG. 7 illustrates an embodiment of the present disclosure forgenerating the Lock Out signal by the TAP itself and by using only theexisting test interface signals.

FIG. 8A illustrates the Lock Out circuit of FIG. 7.

FIG. 8B illustrates the operation of the Unlock state machine of FIG.8A.

FIG. 9 illustrates an embodiment of a system IC including cores 1-N thatuse the dual mode TAP/STP interface of the present disclosure.

FIG. 10A illustrates a test architecture according to another embodimentof the disclosure.

FIG. 10B illustrates a bypass register used in FIG. 10A.

FIGS. 10C and 10D illustrate multiplexers used in FIG. 10A.

FIG. 11 illustrates a second embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present disclosure.

FIG. 12A illustrates a test architecture according to another embodimentof the disclosure.

FIG. 12B illustrates a multiplexer used in FIG. 12A.

FIG. 13 illustrates a third embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present disclosure.

FIG. 14 illustrates an embodiment of the disclosure having aconfigurable scan circuit.

FIG. 15 illustrates a fourth embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present disclosure.

FIG. 16 illustrates another embodiment of the disclosure having aconfigurable scan circuit.

FIG. 17 illustrates a fifth embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present disclosure.

FIG. 18 illustrates a sixth embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present disclosure.

FIG. 19A illustrates a test architecture according to another embodimentof the disclosure.

FIG. 19B illustrates a scan cell used in FIG. 19A.

FIGS. 19C-19E illustrate multiplexers used in FIG. 19A.

FIG. 20A illustrates an example timing diagram of STP controlled scanoperations to the boundary scan register of FIG. 19A.

FIG. 20B illustrates a circuit for producing the STPUC signal used inFIG. 19D.

FIG. 20C illustrates boundary and internal scan cells.

FIG. 21 illustrates an IC containing cores having and TAP/STP interfacecoupled to a tester controlled scan path and a boundary scar register.

FIG. 22 illustrates an IC or core being tested via the TAP/STPinterface.

FIG. 23 illustrates an arrangement for connecting multiple TAP domainswithin an IC to a single scan path.

FIG. 24 illustrates a structure for connecting multiple TAP domainswithin an IC.

FIG. 25 illustrates circuitry for providing the TMSICT, TMSCIT, andTMSCNT signals in FIG. 24.

FIG. 26 illustrates circuitry for providing the TDIICT, TDICIT, andTDICNT signals in FIG. 24.

FIG. 27 illustrates circuitry for multiplexing the TDOICT, TDOCIT, andTDOCNT signals in FIG. 24 to the TDO output.

FIG. 28A illustrates the structure of the TLM of FIG. 24.

FIG. 28B illustrates the structure of instruction register of FIG. 28A.

FIG. 29 illustrates various arrangements of TAP domain connectionsduring 1149.1 instruction scan operations.

FIG. 30 illustrates that during 1149.1 data scan operations the TLM 2403of FIG. 24 is configured to simply form a connection path between theoutput of the selected TAP domain arrangement and the IC's TDO pin.

FIG. 31 illustrates how the structure of the TLM architecture of FIG. 24may be adapted to support TAP/STP domains instead of TAP domains.

FIGS. 32 and 33 represent the TAP/STP domain signal name substitutionfor the TAP domain signal names in the TMS gating circuitry and TDImultiplexing circuitry of the input circuitry of FIG. 31.

FIG. 34 represents the TAP/STP domain signal name substitution for theTAP domain signal names of the output circuitry of FIG. 31.

FIG. 35A illustrates the TLM of FIG. 31.

FIG. 35B illustrates the instruction register of FIG. 35A.

FIG. 36 illustrates various arrangements of TAP/STP domain connectionsduring 1149.1 TAP instruction scan operations using the TAP/STParchitecture of FIG. 31.

FIGS. 37 and 38 illustrate that during 1149.1 data scan operations theTLM 3103 is configured to form a connection path between the output ofthe selected TAP/STP domain arrangement and the IC's TDO/SO pin.

FIGS. 39 and 40 illustrate modified embodiments of the structure of FIG.31.

FIGS. 41-43 illustrate various arrangements of domain connections usingthe architecture of FIG. 40.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides a method and structure for merging thecore TAPs and STPs into a single test interface and accessing the mergedTAP and STP test interface using a single internal scan path wiring bus.Further the present disclosure provides a method and structure forselectively accessing one or more merged TAP and STP test interfaces viaa single IC test pin interface and a single IC scan path wiring bus.

FIG. 5A illustrates the method and structure of the present disclosureto utilize a single IC test interface and a single internal scan pathwiring bus to provide access to the internal scan circuit 501 fromeither the TAP or STP of FIG. 4. In FIG. 5A, the internal scan circuit501 and TAP circuit 502 share a common SI and TDI test input connection(TDI/SI) and a common SO and TDO test output (TDO/SO) connection. Alsothe internal scan circuit 501 and TAP circuit 502 share a common TMS andCS test input connection (TMS/CS). Further, the TCK input is shared as aclock for both the internal scan circuit 501 and TAP circuit 502. Toenable the sharing of the test interface signals, an AND gate 503 isincluded in the TMS/CS signal path to the TAP to allow enabling the TAPor disabling the TAP. Also a 3-state buffer 506 is placed on the SOoutput of the scan circuit 501, and connection circuitry 505 is added asan interface to the scan circuitry. A signal called Lock Out is input tothe AND gate 503 and buffer 506 via OR gate 512. OR gate 512 inputs theLock Out signal and a SO enable signal from the TAP's instructionregister via bus 504. When Lock Out is high, the TAP is enabled toreceive and respond to the TMS/CS and the output of the 3-state buffer506 is disabled via OR gate 512. When Lock Out is low, the TAP isdisabled from receiving the TMS/CS signal. If the SO enable signal frombus 504 is low, the low on the Lock Out signal also enables the outputof the 3-state SO buffer 506, via OR gate 512.

In FIG. 5A, the internal scan register of the internal scan circuit 501remains a data register within the TAP data registers section, asevidenced by the serial input 101, serial output 104, and control 511connections to the TAP 502. Therefore, scan circuit 501 remainsconventionally accessible as one of the data registers within the TAP'sdata register section, as previously shown and described in regard toFIGS. 1A and 1C. In general the present disclosure maintains TAP accessto any data register which is also rendered accessible by the STPinterface, including but not limited to all other data registers shownin FIGS. 1A and 1D-1G. Thus the present disclosure provides a dual modetest access port for accessing data registers using either the TAP orSTP interfaces.

Assuming the TAP 502 is initially enabled but that access to theinternal scan circuit 501 is desired using the STP interface, thefollowing sequence would occur. The TAP would be accessed to load a scantest instruction into its instruction register. The scan testinstruction would be defined according to the present disclosure tooutput control on bus 504 of the present disclosure to connectioncircuitry 505 and OR gate 512 of the present disclosure. As seen in FIG.5A, one of the instruction control output signals that passes throughconnection circuit 505 to be input to the scan circuit 501 is the SEinput. As mentioned in regard to FIG. 3A, the SE input is conventionallyinput using an IC pin. However, the present disclosure generates the SEsignal internally using an instruction which eliminates the need for adedicated IC pin to input the SE signal. The instruction control on bus504 may also be output to other circuits not shown in FIG. 5A tocondition them for the pending internal scan test operation. Theinstruction control output occurs during the Update-IR state of FIG. 2.Simultaneous with the instruction control output, the Lock Out signaltransitions from a logic high to a logic low. AND gate 503 passes theLock Out logic low to the TAP's TMS input and OR gate 512 passes theLock Out logic low to the control input of the SO buffer 506. The TAPcontroller responds to the logic low on the TMS input to transition fromthe Update-IR state to the Run Test/Idle state, as seen in FIG. 2. Alsothe logic low on the Lock Out signal and the logic low on the SO enablesignal to OR gate 512 enables the SO buffer 506 to drive the TDO/SOoutput. Note that if the instruction loaded into the instructionregister does not set the SO enable signal to a logic low, the SO outputbuffer 506 would not be enabled by a the logic low on Lock Out, sincethe output of OR gate 512 would remain at a logic high state.

After the above sequence is performed, the TAP is disabled by the LockOut signal to its Run Test/Idle state (FIG. 2). While the TAP is forced,by the Lock Out signal, to remain in the Run Test/Idle state, the TMS/CSsignal can be used as the CS signal of FIG. 3A to control the captureand shift operations of the scan circuit 501. While the TAP is disabled,its TDO output buffer is disabled to allow the enabled SO buffer 506 todrive out on the TDO/SO output. In preparation for an STP controlledscan test, the TCK signal is connected to the scan circuit's CK inputusing, for example, a multiplexer as shown in FIG. 5C, and the TMS/CSsignal is connected to the scan circuit's CS input using, for example, amultiplexer as shown in FIG. 5D. The CKSEL and CSSEL control inputs tothe multiplexers of 5C and 5D come from the instruction output controlon bus 504. The CK and CS outputs from the multiplexers of 5C and SD areconnected to the individual scan cells of the internal scan register ofscan circuit 501 as shown in FIG. 5B. The internal scan registercomprises multiple ones of the FIG. 5B scan cells connected seriallybetween their serial input (SI) and serial output (SO). The CK and CSmultiplexing circuitry reside in connection circuitry 505. The FCK inputto connection circuitry 505 is the functional clock source. During theSTP controlled scan test operation, scan circuit 501 receives the TMS/CSinput as the CS input of FIG. 3A and the TCK input as the CK input ofFIG. 3A to capture data and shift data from TDI/SI to TDO/SO of FIG. 5A.Thus, when setup by the sequence described above, the scan circuit 501is rendered scan testable via the STP interface as described previouslyin regard to FIG. 3A.

After the above mentioned STP scan test operation is complete, the LockOut signal returns to a logic high state to disable the SO buffer 506and to enable the TAP to once again respond to TMS input. When Lock Outgoes high, a new instruction may be scanned into the TAP instructionregister to place the scan circuit 501 back into its functionaloperation mode or to start another type of test or other operation.

As seen in FIG. 5C, the CK output maybe connected to the FCK, the TCK,Clock-DR (TAP), or to a static OFF state. During normal functionaloperation, CK is connected to FCK. During STP controlled internal scantesting CK may be connected to the TCK as described above. Alternativelyduring STP controlled internal scan testing, the CK may be connected tothe FCK to allow the scan test to operate using the functional clocksource. During TAP controlled access to the internal scan circuit 501,say during an in-circuit emulation/debug or TAP controlled internal scanoperation, CK is connected to the Clock-DR signal of the TAP controller.During shut down operations, say during times when one or morecores/circuits need to be disabled while other cores/circuits aretested, the CK to the disabled cores/circuits may be connected to thestatic OFF input to stop all clocking activity in the disabledcores/circuits.

FIG. 6 is provided to simply illustrate that the source of the Lock Outsignal could come from an additional IC pin or core terminal, or from aregister (R) or other circuit embedded within the system IC.

FIG. 7 illustrates a method and structure for generating the Lock Outsignal by the TAP itself and by using only the existing test interfacesignals (TDI/SI, TMS/CS, TCK, TRST, and TDO/SO). The advantage ofproducing the Lock Out signal using only the pre-existing test interfacesignals is that no additional pin/terminal is required on the IC/core,and that testers that drive IC TAP interfaces today can be used to setthe Lock Out signal without having to provide an additional hardwaretest interface signal to drive the Lock Out pin/terminal signal of FIG.6. As seen in FIG. 7, the modification to include a TAP generated LockOut signal involves: (1) providing a TAP Lock circuit 508, (2) providingand connecting a Lock Input signal 507 to the TAP Lock circuit 508 frominstruction register output bus 504, (3) providing an instruction toproduce the Lock Input signal output onto bus 504, (4) connecting theUpdate-IR signal output from the TAP controller to the Lock Out circuit508, (5) connecting the TCK input to the Lock Out circuit 508, (6)connecting the TMS/CS input to the Lock Out circuit 508, and (7)connecting the TRST input to the Lock Out circuit 508. The Lock Inputsignal 507 is output from the instruction register such that the TAPcontroller Update-IR signal may clock it into the Lock Out circuit 508during the Update-IR state of FIG. 2, i.e. the Lock Input signal 507 isoutput from the instruction register prior to the occurrence of the TAPcontroller's Update-IR signal that occurs at the end of each instructionscan operation.

FIG. 8A illustrates in detail the Lock Out circuit 508. The Lock Outcircuit consists of a D-FF 801 for receiving the Lock In signal 507 atits data input, the Update-IR signal at its clock input, and a resetinput via AND gate 804. The Lock Out circuit also includes an Unlockstate machine 803. The Unlock state machine receives TCK as a clockinput, TMS/CS as a data input, TRST as reset input, and the data outputof D-FF 801 as an enable input. The Unlock state machine outputs anUnlock signal to the reset input of the D-FF 801, via AND gate 804. TRSTis also input to the reset input of D-FF 801 via AND gate 804. Inresponse to the Update-IR signal from the TAP controller, the D-FFoutputs the state of the Lock In input to the Unlock state machine andto inverter 802 which outputs the Lock Out output signal. As long as thedata output from D-FF 801 is low, the Unlock state machine is disabledand the Lock Out output from inverter 802 is high. While Lock Out ishigh, the TAP is enabled to respond to the TMS/CS input via AND gate503, and the SO buffer 506 is disabled as previously described. When aninstruction is loaded into the TAP's instruction register to enable anSTP controlled scan test operation, the Lock Input will be set high suchthat, in response to the Update-IR signal, the data output of the D-FFgoes high. A high on the data output of the D-FF enables the Unlockstate machine and sets Lock Out from inverter 802 low. A low on Lock Outdisables the TAP to the Run Test/Idle state and the enables the SObuffer 506 as previously described. Also the instruction outputs controlvia bus 504 to connection circuit 505 to input the SE signal to scancircuit 501 and to form appropriate CS and CK connections to scancircuit 501 for the STP controlled scan test operation, and to set theSO enable signal to OR gate 512 low, again as previously described.

While Lock Out is low, the Unlock state machine is enabled to monitorthe state of the TMS/CS signal during each TCK period. During the STPcontrolled test operation, the TMS/CS signal input to scan circuit 501goes low to capture data then goes high to shift data from TDI/SI toTDO/SO. The number of times the Unlock state machine detects a low onTMS/CS is therefore only during the times when the scan circuitry 501 isperforming a capture operation. Conventionally, the STP operates tocapture data using one TCK period, then shifts data using multiple TCKperiods. The Unlock state machine exploits this conventional STP captureand shift timing to devise a simple method of escaping from the STPcontrolled mode to re-enter the TAP controlled mode. The operation ofthe Unlock state machine and its escape sequence is best understood byinspection of the Unlock state diagram of FIG. 8B.

As seen in FIG. 8B, the Unlock state machine comprises Idle 1, Idle 2,Sequence 1-3, and Unlock TAP states. When first enabled by the dataoutput of D-FF 801 going high, the Unlock state machine will be in theIdle 1 state and will remain in the Idle 1 state while TMS/CS is low.Holding TMS/CS low to maintain the Idle 1 state when the Unlock statemachine is first enabled, provides time for the test interface andarchitecture to switch from TAP controlled operation to STP controlledoperation. For example, during the Update-IR state that enables theUnlock state machine in the Idle 1 state, the CKSEL and CSSEL controlsignals are input to the CK and CS multiplexers of FIGS. 5C and 5D tocouple CK to TCK and CS to TMS/CS, and the Lock Out signal enables SObuffer 506. By holding TMS/CS low to remain in the Idle 1 state for acertain number of TCKs, the CK and CS multiplexers are given time toswitch, the scan circuit 501 is given time to respond to the CK and CSswitch, and the SO buffer 506 is given time to become enabled. After theCK and CS switch and SO buffer enable time, the scan circuit 501 willoperate in the capture mode since it will be receiving CK inputs (viaTCK) while the CS input is low (via TMS/CS being low).

Applying a high level on TMS/CS will initiate the first shift operationthrough scan circuit 501 from TDI/SI to TDO/SO and cause the Unlockstate machine to transition from the Idle 1 state to the Idle 2 state.The Idle 2 state is maintained while TMS/CS is high to complete thefirst shift operation. At the end of the shift operation, a low level isapplied to TMS/CS to initiate a capture operation and to cause theUnlock state machine to transition from the Idle 2 state to the Sequence1 state. At the end of the capture operation, a high level is applied toTMS/CS to initiate the second shift operation and to transition theUnlock state machine from the Sequence 1 state to the Idle 2 state. Thehigh on TMS/CS maintains the second shift operation until the nextcapture operation is required, at which time a low level will be appliedon TMS/CS. The above shift/capture operation and corresponding Idle2/Sequence 1 state sequence repeats until the STP controlled test ofscan circuit 501 has been completed. At the end of the last shiftoperation of the STP controlled test, a low level is applied andmaintained on TMS/CS which causes the Unlock state machine to transitionfrom the Idle 2 state, through the Sequence 1-3 state, through theUnlock TAP state, to re-enter the Idle 1 state. Passing through theUnlock TAP state, the Unlock state machine outputs an Unlock signal tothe reset input of D-FF 801, via AND gate 804. In response to the Unlocksignal, the data output of the D-FF goes low, which disables the Unlockstate machine to its Idle 1 state and sets the Lock Out from inverter802 high. When Lock Out goes high, the SO buffer 506 is disabled and theTAP controller is once again enabled to respond to the TMS/CS input viaAND gate 503 to provide control of the test architecture. The enabledTAP controller will remain in the Run Test/Idle state if TMS/CS remainslow, or, as seen in FIG. 2, it may transition from the Run Test/Idlestate to perform a data register scan operation, an instruction registerscan operation, or enter the Test Logic Reset state.

In some variances of STP controlled testing, back to back captureoperations may occur between shift operations to support delay testingof the scan circuit 501. The Unlock state machine is designed to allowfor this back to back capture (i.e. two consecutive lows on TMS/CS)possibility as seen in state transitions from Idle 2 to Sequence 1 toSequence 2, and back to Idle 2. In fact, as seen in the state diagram,the Unlock state machine can handle up to three back to back capture(i.e. three consecutive lows on TMS/CS) operations without Unlocking theTAP, as seen by state transitions from Idle 2 to Sequence 1 to Sequence2 to Sequence 3, and back to Idle 2. In general, Unlock state machinesare designed to comprehend the total number of consecutive TMS/CS lowsignals required to perform any given STP controlled test operation. TheSTP controlled test operation will be maintained as long as the numberof consecutive TMS/CS low signals is less than or equal to that totalnumber. If the number of consecutive TMS/CS low signals exceeds thattotal number, the Unlock state machine will disable STP control andreinstate TAP control of the test architecture, as described above.

FIG. 9 illustrates a system IC including cores 1-N that use the dualmode TAP/STP interface of the present disclosure. In this example, eachTAP/STP interface includes a TAP lock circuit 508 of FIGS. 7, 8A, and8B, so only the IEEE 1149.1 standard TDI, TDO, TMS, TCK, and TRST signalpins are required on the IC for selecting the TAP or STP mode of theTAP/STP interface, i.e. the Lock Out signal pin of FIG. 6 is notrequired. A first advantage of the present disclosure is that the systemIC of FIG. 9 only has to provide a single internal scan path wiring bus910 to the cores for performing both TAP controlled and STP controlledoperations. In contrast, the system IC of FIG. 4 had to provide twointernal scan path wiring buses 410 and 420 to the cores, one for theTAP and another for the STP. A second advantage of the presentdisclosure is that the tester connected to the system IC of FIG. 9 canselectively perform either TAP or STP controlled operations using thesame standard IC test pins defined in the IEEE 1149.1 standard, i.e.TDI, TDO, TMS, TCK, and TRST. In contrast, a tester connected to thesystem IC of FIG. 4 had to provide two separate IC test pin interfacesto the IC, one for the TAP and another for the STP.

At power up of the system IC of FIG. 9, all core TAP/STP interfacespreferably default to the TAP control mode so that the core TAPs can beaccessed for scanning in instructions to setup test, emulation,programming, or other TAP controlled operations. When STP controlledscan testing is required in all the cores, a TAP instruction scan willbe performed to load an STP enable instruction into each core's TAPinstruction register, as described in regard to FIGS. 5A, 6A, 7, and 8A.Once the instruction is updated during the Update-IR state of FIG. 2,all core TAP/STP interfaces switch from the TAP control mode to the STPcontrol mode. Assuming each core has an internal scan circuit 501 asdescribed in FIGS. 5-7, a tester may perform scan testing on all thedaisy-chained internal scan circuits 501 of cores 1-N via the singletest pin interface and single scan path wiring bus 910. At the end ofthe STP controlled test operation, TAP control of the core TAP/STPinterfaces can be reinstated by setting the TMS/CS signal to a statethat will disable the TAP lock circuits 508 to their Idle 2 state, asdescribed in FIGS. 8A and 8B.

In FIG. 9, a dotted line connection 904 is shown formed between thecores to illustrate another example implementation of the presentdisclosure whereby a single TAP lock circuit of one core (Corel) is usedto provide Lock Out signals to other cores (Cores 2-N) which do notthemselves have TAP lock circuits. In this example, the TAP lock circuitof Core 1 is equipped with an output terminal 901 for outputting theLock Out signal to connection 904 and Cores 2-N are equipped with inputterminals 902 and 903 for inputting the Lock Out signal from Core 1.Core 1 would utilize the FIG. 7 TAP/STP interface which includes the TAPlock circuit. Cores 2-N would utilize the FIG. 6 TAP/STP interface whichdoes not include the TAP lock circuit, but rather inputs the Lock Outsignal via a core terminal. The operation of this alternate realizationof the present disclosure to switch between TAP and STP controlled modesis the same as previously described. The use of a single TAP lockcircuit to generate the Lock out signal to a plurality of TAP/STPinterfaces, as shown in FIG. 9, should be understood to be an alternatemethod of implementing the present disclosure in all examples describedherein. In some implementations, the use of one TAP lock circuit in oneTAP/STP interface to generate the Lock out signal to other TAP/STPinterfaces as shown in FIG. 9 may be preferred since it eliminates theneed for each TAP/STP interface to have its own TAP lock circuit.

As mentioned in the FIG. 9 STP controlled test operation above, allcores 1-N were assumed to have a scan circuit 501 so that all the scancircuits 501 could be daisy-chained onto the scan path wiring bus 910and tested at the same time. However, not all the cores may have a scancircuit 501. Therefore a method and structure is needed to allow STPcontrolled daisy-chaining of the core TAP/STP interfaces onto scan pathwiring bus 910 when all the cores do not have scan circuits 501, or whentesting of only a selected one or more of the scan circuits 501 isdesired. The following description of FIGS. 10A-D and 11 provides amethod and structure of the present disclosure for selecting the bypassregister of the TAP/STP interfaces to be inserted into the scan pathwiring bus 901 to provide an alternate daisy-chain arrangement betweenthe cores.

FIG. 10A illustrates a test architecture similar to that described inregard to FIG. 7. The difference between the test architecture of FIG.10A and FIG. 7 is that the TAP's bypass register 1001 of FIG. 1A hasbeen selected for STP controlled scanning instead of the scan circuit501 of FIG. 7. An example bypass register is shown in FIG. 10B. Theserial input of the bypass register 1001 is connected to TDI/SI viaconnection 101. The serial output of the bypass register is connected tothe TAP data registers section via connection 108 to maintainconventional TAP controlled access as described in regard to scancircuit 501 of FIG. 5A. The serial output of the bypass register is alsoselectively connectable to the TDO/SO output via SO buffer 1005.Connection circuitry 1004 is provided for connecting the TAPcontroller's Clock-DR and Capture-DR to the bypass registers CK and CSinputs during TAP controlled operation, or for connecting the bypassregister CK and CS inputs to TCK and TMS/CS during STP controlledoperation. An example CK multiplexer is shown in FIG. 10C, and anexample CS multiplexer is shown in FIG. 10D. Both multiplexers reside inconnection circuit 1004 and both receive bypass register CK and CSselection signals CKSEL and CSSEL from the TAP instruction register viabus 504.

The process for selecting the bypass register between TDI/SI and TDO/SOand switching the TAP/STP interface into the STP controlled mode issimilar to that described for selecting the scan circuit 501 of FIGS.5-7. While in the TAP controlled mode, a bypass instruction is scannedinto and updated from the instruction register. The outputs from theinstruction register are input to the TAP lock circuit 508, connectioncircuit 1004, and OR gate 1006, via bus 504. In response to the signalsfrom bus 504, the TAP lock circuit outputs a low on Lock Out whichdisables the TAP and enables SO output buffer 1005 via OR gate 1006. TheLock Out signal is allowed to pass through OR gate 1006 since the bypassregister SO enable signal to OR gate 106 from the instruction registeris set low. Also, in response to the signals from bus 504, connectioncircuitry 1004 connects TMS/CS to the bypass register's CS input and TCKto bypass register's CK input. It should be noted that the SO buffer1005, OR gate 1006, and connection circuitry 1004 is separate from theSO buffer 506, OR gate 512, and connection circuitry 505. Also thebypass instruction control signals to connection circuitry 1004, SObuffer 1005, and OR gate 1006 is separate from the scan test instructioncontrol signals to connection circuitry 505, SO buffer 506, and OR gate512. In general this is true for all data registers (i.e. internal scan,bypass, boundary scan, ISP, and ICE data registers of FIG. 1A) that arerequired to be individually connected between TDI/SI and TDO/SO andoperated in the STP control mode. When the bypass SO buffer 1005 isenabled to drive out on TDO/SO, all other SO buffers (for example thescan circuit SO buffer 506 of FIG. 7) will be disabled to avoidcontention during STP controlled testing.

FIG. 11 illustrates an example IC containing cores I-N. In this example,all the TAP/STP core interfaces have been switched to the STP controlledmode. Cores land 3-N have had their bypass registers 1001 connectedbetween their TDI/SI and TDO/SO terminals, as described in the processabove. Core 2 has had its scan circuit 501 connected between its TDI/SIand TDO/SO terminals, as described in regard to FIGS. 5-7. FIG. 11illustrates an example of how to daisy-chain cores onto scan path wiringbus 910 to where cores not being tested (Cores 1, 3-N) select theirbypass registers 1001 to be in the daisy-chain scan path 910 while coresbeing tested (Core 2) select their scan circuit 501 to be in thedaisy-chain scan path 910. During the STP controlled capture operationthe bypass registers 1001 of Cores 1 and 3-N capture a logic low, asshown in FIG. 10B, and the scan circuit 501 of Core 2 captures testresponse data. During the STP controlled shift operation the bypassregisters 1001 of Cores 1 and 3-N shift data along the scan path 910from the their TDI/SI input to TDO/SO output terminals as shown in FIG.10B, and the scan circuit 501 of Core 2 shifts data along scan path 910from its TDI/ST input to TDO/SO output terminals.

FIG. 12A illustrates another example configuration of the presentdisclosure whereby the serial input and serial output of scan circuit501 are multiplexed to a test pattern source and a test patterndestination, respectively. The test pattern source 1208 could beinternally generated by a circuit within the IC, such as a linearfeedback shift register, or it could be externally input from a testervia an IC pin. The test pattern destination 1209 could be internallyprocessed by a circuit within the IC, such as a signature analyzer, orit could be externally output to a tester via an IC pin. The TAP/STPinterface is similar to that described in FIGS. 5-7. The key differencesbetween the TAP/STP interface of FIG. 12A and the TAP/STP interfaces ofFIGS. 5-7 include; (1) multiplexer 1201 is provided to selectivelyconnect the serial input of scan circuit 501 to either source 1208 orTDI/SI 101, (2) multiplexer 1203 is provided to selectively connect theserial output of scan circuit 501 to destination 1209 in substitution offunctional signal 1203, (3) the FCK signal 1206 is made available at acore terminal or IC pin to serve as the CK input to scan circuit 501,(4) a capture shift signal source (CSs) is provided and made availableat a core terminal or IC pin to serve as the CS input to scan circuit501, and (5) a source/destination test instruction is provided that,when shifted into and updated from the TAP instruction register,provides control on bus 504 to multiplexers 1201 and 1202 and toconnection circuitry 1210, to connect scan circuit 501 to the source,destination, FCK, and CSs signals. While a multiplexer 1202 is shown forconnecting the serial output of scan circuit 501 to the destination1209, in substitution of a functional signal 1203, the serial output maybe coupled to the destination using a source/destination instructioncontrolled 3-state buffer as well. For cores, the serial output fromscan circuit 501 may have a dedicated output terminal for connecting todestination 1209.

Connection circuitry 1210 comprises a CK multiplexer like that shown inFIG. 5C to allow the FCK 1206 signal to be coupled to the scan circuit's501 CK input in response to the source/destination test instructionoutput on bus 504. The connection circuitry 1210 also includes the CSmultiplexer of FIG. 12B, to allow CSs 1207 to be coupled to the scancircuits CS input, in response the source/destination test instructionoutput on bus 504. In addition to the test source and destination testmode configuration described above, the TAP/STP interface of FIG. 12Amaintains the previously described TAP and STP controlled test modes toscan circuit 501. Also it is should be understood that the new sourceand destination test mode operates independent of the TAP/STP interface,once the source/destination test instruction has been loaded. Further,the TAP/STP interface may be placed in either the TAP controlled or STPcontrolled mode by the source/destination test instruction withouteffecting the operation of the source and destination tests. Indeed, twosource/destination test instructions may be used. A firstsource/destination test instruction may configure scan circuit 501 forsource and destination testing as described above and leave the TAP/STPinterface in the TAP controlled mode. A second source/destination testinstructions may configure scan circuit 501 for source and destinationtesting as described above and place the TAP/STP interface into the STPcontrolled mode.

FIG. 13 illustrates an example IC containing cores 1-N having TAP/STPinterfaces coupled to scan path 910. Each core includes the source anddestination test mode described in regard to FIG. 12A. When thesource/destination test instruction is loaded into the cores, each coreconnects its source input 1208 to a respective internal or externalsource 1301, 1303, 1305, connects its destination output 1209 to arespective internal or external destination 1302, 1304, 1306, connectsits CSs input 1207 to a respective internal or external CSs 1307, 1309,1311, and connects its FCK input 1206 to a respective internal orexternal FCK 1308, 1310, 1312. Once the source and destinationconfiguration is made, the scan circuits 501 of the cores 1-N can betested. During the test, the core's CSs 1207 and FCK 1206 inputs areoperated to capture data and shift data through the scan circuits 501from the source inputs 1208 to the destination outputs 1209. SeparateCSs 1307, 1309, 1311, FCKs 1308, 1310, 1312, sources 1301, 1303, 1305,and destinations 1302, 1304, 1306 may be used for each core forasynchronous core testing, or alternately each core may be interfaced tothe same CSs and FCK to allow communication between the core 1-N sourcesand destinations to occur synchronously. While source and destinationtesting occurs, the core's TAP/STP interfaces may be accessed via scanpath 910 without interfering with the source destination testing. Alsothe core TAP/STP interfaces may be accessed using either TAP control orSTP control.

FIG. 14 illustrates another example configuration of the presentdisclosure whereby a configurable scan circuit 1401 is substituted forscan circuit 501. The logic circuitry of scan circuit 1401 can be testedin a first configuration where the scan circuit 1401 scan path isconfigured into a single scan register, or in a second configurationwhere the scan circuit 1401 scan path is configured into separateparallel scan registers 1-N. When placed in the first configuration, thesingle scan register can be coupled between TDI/SI and TDO/SO and testedusing either the TAP or STP as previously described for scan circuit501. When placed in the second configuration, the serial inputs of theseparate parallel scan registers 1-N are coupled to parallel sources 1-N1409 via multiplexers 1402-1403, and the serial outputs of the separateparallel scan registers 1-N are coupled to parallel destinations 1-N1408 via multiplexers 1405-1406. The sources 1409 and destinations 1408can be internally or externally provided, as described in regard to FIG.12A.

The key differences between the TAP/STP interface of FIG. 14 and TAP/STPinterfaces of FIGS. 5-7 and 12A include; (1) multiplexer 1402 isprovided to selectively connect the serial input of parallel scanregister N to either source N or the serial output of parallel scanregister N−1, or in this example where N=2, to the serial output ofparallel scan register 1, (2) multiplexer 1403 is provided toselectively connect the serial input of parallel scan register 1 toeither source 1 or TDI/SI 101, (3) multiplexer 1405 is provided toselectively connect the serial output of parallel scan register N todestination N in substitution of functional a signal 1410, (4)multiplexer 1406 is provided to selectively connect the serial output ofparallel scan register 1 to destination 1 in substitution of afunctional signal 1411, (5) a serial test instruction is provided that,when shifted into and updated from the TAP instruction register,provides control on bus 504 to multiplexers 1402-1403 and 1405-1406 toserially connect parallel scan registers 1-N into a single scan path forTAP or STP access via TDI/SI and TDO/SO, (6) a parallel test instructionis provided that, when shifted into and updated from the TAP instructionregister, provides control on bus 504 to multiplexers 1402-1403 and1405-1406 to connect the parallel scan registers 1-N to sources 1-N anddestinations 1-N for TAP or STP controlled access via sources 1-N anddestinations 1-N.

In response to either of the above serial or parallel test instructions,connection circuit 505 receives control on bus 504 to operate the scanregisters of scan circuit 1401 in either the TAP or STP controlled mode,as previously described. As with the source/destination test instructionof FIG. 12A, both TAP and STP controlled versions of the serial testinstruction and a parallel test instruction may be provided to allow theserial and parallel configurations of scan circuit 1401 to be controlledby either the TAP or STP.

FIG. 15 illustrates an example IC containing cores 1-N having TAP/STPinterfaces coupled to scan path 910. Each core includes the serial andparallel scan test access modes to scan circuit 1401 as described inregard to FIG. 14. When the serial test instruction is loaded into thecores, the scan circuits 1401 are accessed and tested using only thescan path 910 signals, and using either TAP or STP control. Theoperation of the serial test instruction in FIG. 15 to testdaisy-chained scan circuits 1401 is similar in operation to the scantest instruction of FIG. 9 to test daisy-chained scan circuits 501. Whenthe parallel test instruction is loaded into the cores, the scancircuits 1401 of cores 1-N are coupled to source 1-N inputs 1409 anddestination 1-N output 1408. As seen in FIG. 15, the source 1-N input ofCore 1 is connected to a source 1501 which can be either internally orexternally provided. The destination 1-N output of Core 1 is connectedto the source 1-N input of Core 2. The destination 1-N output of Core 2is connected to the source 1-N input of Core N. The destination 1-Noutput of Core N is connected to destination 1502 which can be eitherinternally or externally provided. In this arrangement, the scancircuits 1401 of cores 1-N are seen to be daisy-chained on a parallelscan bus beginning at source 1501 and ending a destination 1502. TheTMS/CS and TCK input signals to the core TAP/STP interfaces from scanpath 910 are used to control the capture of data and the shifting ofdata through the daisy-chained scan circuits 1401 from source 1501 todestination 1502. The capturing and shifting of data through thedaisy-chained scan circuits 1401 can be either TAP or STP controlled.

FIG. 16 illustrates another example configuration of the presentdisclosure whereby the configurable scan circuit 1401 FIG. 14 is madecontrollable from the FCK 1206 and CSs 1207 inputs to connectioncircuitry 1210 as described earlier in regard to FIG. 12A. The FIG. 16example maintains the serial and parallel test instruction modesdescribed in regard to FIGS. 14 and 15. Additionally, the FIG. 16example provides a parallel source/destination test instruction thatenables the FCK and CSs inputs to control the capture and shiftoperations of scan circuit 1401. The parallel source/destinationinstruction is similar to the source/destination instruction of the FIG.12A example. The key difference is that scan circuit 1401 is connectedto parallel source 1-N inputs 1409 and parallel destination 1-N outputs1408, as opposed to the scan circuit 501 being connected to a singlesource input 1208 and a single source output 1209.

FIG. 17 illustrates an example IC containing cores 1-N having TAP/STPinterfaces coupled to scan path 910. Each core includes the parallelsource and destination test mode described in regard to FIG. 16. Whenthe parallel source/destination test instruction is loaded into thecores, each core connects its parallel source input 1409 to a respectiveinternal or external parallel source 1701, 1703, 1705, connects itsparallel destination output 1408 to a respective internal or externalparallel destination 1702, 1704, 1706, connects its CSs input 1207 to arespective internal or external CSs 1307, 1309, 1311, and connects itsFCK input 1206 to a respective internal or external FCK 1308, 1310,1312. Once the parallel source and destination configuration is made,the scan circuits 1401 of the cores 1-N can be tested. During the test,the core's CSs 1207 and FCK 1206 inputs are operated to capture data andshift data through the scan circuits 1401 from the source inputs 1409 tothe destination outputs 1408. Separate CSs 1307, 1309, 1311, FCKs 1308,1310, 1312, sources 1701, 1703, 1705, and destinations 1702, 1704, 1706may be used for each core for asynchronous core testing, or alternatelyeach core may be interfaced to the same CSs and FCK to allowcommunication between the core 1-N sources and destinations to occursynchronously. While parallel source and destination testing occurs, thecore's TAP/STP interfaces may be accessed via scan path 910 withoutinterfering with the parallel source destination testing. Also the coreTAP/STP interfaces may be accessed using either TAP control or STPcontrol.

FIG. 18 illustrates an example of how the present disclosure may be usedto simultaneously enable and execute different types of testing ondifferent cores 1-N within an IC. Core 1 has been loaded with thesource/destination test instruction previously described in regard toFIGS. 12A and 13. Core 2 has been loaded with the scan test instructionas previously described in regard to FIGS. 5-9. Cores 3-N have beenloaded with the parallel source/destination test instruction describedin regard to FIGS. 16-17. To setup the test, a single TAP controlledinstruction scan may be performed to load each of the above mentionedtest instructions into the TAP/STP interfaces of each core 1-N.Following the instruction scan, Core 1 is configured for source anddestination testing as described in FIGS. 12A and 13, Core 2 isconfigured for scan testing as described in regard to FIGS. 5-9, andCores 3-N is configured for parallel source and destination testing asdescribed in regard to FIGS. 16-17.

As seen in FIG. 18, the source destination test instruction loaded intoCore 1 selects the bypass register 1001 to be coupled between Core 1'sTDI/SI and TDO/SO terminals. Also the parallel source destination testinstruction loaded into Cores 3-N selects the bypass register 1001 to becoupled between each of the Core 3-N TDI/SI and TDO/SO terminals. Thebypass registers 1001 are selected to allow access to and testing ofscan circuit 501 of Core 2 via scan path 910, while Cores 1 and 3-N arebeing tested using the described source and destinations test methods.To enable access to Core 2's scan circuit 501, the source destinationtest instruction loaded into Core 1 and the parallel source destinationinstructions loaded into Cores 3-N are designed to not only configureCores 1 and 3-N for their respective source and destination testing, butalso to select the bypass register 1001 between TDI/SI and TDO/SO.Additionally, the TAP/STP interfaces of cores 1-N may be selectively setby the instructions to operate the TAP/STP interfaces in either the TAPor STP controlled mode.

If TAP/STP interfaces are set to operate in the TAP controlled mode, thebypass registers of Cores 1 and 3-N and the scan circuit 501 of Core 2will operate on scan path 910 according to the TAP state machine statediagram of FIG. 2. If set to operate in the STP controlled mode, thebypass registers of Cores 1 and 3-N and the scan circuit 501 of Core 2will operate on scan path 910 according to the STP capture and shiftscan protocol. The TAP or STP controlled testing of scan circuit 501 ofCore 2 does not interfere with the source and destination testing ofCores 1 and 3-N because the signals used for the source and destinationtesting (i.e. CSs 1207, FCK 1206, source 1208, destination 1209, source1-N 1407 and destination 1-N 1408) are separate from the scan path 910signals (i.e. TDI/SI, TMS/CS, TCK, TRST, and TDO/SO). Therefore thecores of FIG. 18 may be tested in parallel using the three differenttest methods illustrated and described. In general, FIG. 18 illustrateshow the TAP/STP interface of the present disclosure and the instructionsdefined for the TAP/STP interfaces may be used to allow scan path 910 tobe used for TAP or STP controlled testing simultaneous with testingperformed by signals separate from the TAP/STP interface signals.

FIG. 19A illustrates a test architecture similar to that described inregard to FIG. 7. The difference between the test architectures of FIG.19A and FIG. 7 is that the TAP's boundary scan register 1901 of FIGS. 1Aand 1F has been selected for STP controlled scanning instead of the scancircuit 501 of FIG. 7. An example boundary scan cell is shown in FIG.19B. The boundary scan cell receives a functional input (FI), a serialinput (SI) input, CS input, CK input, update control (UC) input, and amode input. The boundary scan cell outputs a functional output (FO) anda serial output (SO). The mode control input comes from the TAPinstruction register and allows coupling FI to FO during functionaloperation, or coupling FO to the output of the update FF 1904 duringtest operation. The multiplexer and FF combination 1905 provides forcapturing Fl data and shifting data from SI to SO in response to the CSand CK signals. Update FF 1904 loads data from FF 1905 in response tothe UC signal. The boundary scan register comprises multiple ones of theboundary scan cells of FIG. 19B connected serially between their SI andSO. All the boundary scan cells are commonly connected to the mode, CS,CK, and UC signals. The serial input of the boundary scan register 1901is connected to TDI/SI via connection 101. The serial output of theboundary scan register is connected to the TAP data registers sectionvia connection 107 to maintain conventional TAP controlled access to theboundary scan register, as mentioned in regard to FIG. 5A. The serialoutput of the boundary scan register is also selectively connectable tothe TDO/SO output via SO buffer 1902. Connection circuitry 1907 isprovided for connecting the TAP controller's Clock-DR, Capture-DR, andUpdate-DR to the boundary scan register's CK, CS and UC inputsrespectively during TAP controlled operation, or for connecting theboundary scan register's CK, CS, and UC inputs to TCK, TMS/CS, and a STPupdate control (STPUC) signal respectively during STP controlledoperation. The STPUC signal will be described in more detail in regardto FIG. 20AC. An example CK multiplexer is shown in FIG. 19C, an exampleUC multiplexer is shown in FIG. 19D, and an example CS multiplexer isshown in FIG. 19E. All multiplexers reside in connection circuit 1907and all receive boundary scan register CK, CS, UC selection signalsCKSEL, CSSEL, and UPSEL from the TAP instruction register via bus 504.

The process for selecting the boundary scan register between TDI/SI andTDO/SO and switching the TAP/STP interface into the STP controlled modeis similar to that described for selecting the scan circuit 501 of FIGS.5-7. While in the TAP controlled mode, a boundary scan instruction isscanned into and updated from the instruction register. The outputs fromthe instruction register are input to the TAP lock circuit 508,connection circuit 1907, and OR gate 1903, via bus 504. In response tothe signals from bus 504, the TAP lock circuit outputs a low on Lock Outwhich disables the TAP and enables SO output buffer 1902 via OR gate1903. The Lock Out signal is allowed to pass through OR gate 1903 sincea boundary scan register SO enable signal to OR gate 1903 from theinstruction register is set low. Also, in response to the signals frombus 504, connection circuitry 1907 connects TMS/CS to the boundary scanregister's CS input, the TCK to boundary scan register's CK input, andthe STPUC signal to the boundary scan register's UC input. Again, itshould be noted that the SO buffer 1902, OR gate 1903, and connectioncircuitry 1907 is separate from the SO buffers 506 and 1005, OR gates506 and 1005, and connection circuits 505 and 1004 of FIGS. 5A and 10A.Also the boundary scan instruction control signals to connectioncircuitry 1907, SO buffer 1902, and OR gate 1903 is separate from thescan test instruction and bypass instruction control signals toconnection circuitry 505 and 1004, SO buffers 506 and 1005, and OR gates512 and 1006. When the boundary scan register SO buffer 1902 is enabledto drive out on TDO/SO, all other SO buffers 506 and 1005 are disabledto avoid contention during STP controlled boundary scan testing.

FIG. 20A illustrates an example timing diagram of STP controlled scanoperations to the boundary scan register 1901 of FIG. 19A. During STPcontrolled operations, the boundary scan register CS input is driven byTMS/CS via the multiplexer of FIG. 19E, the CK input is driven by TCKvia the multiplexer of FIG. 19C, and the UC input is driven by STPUC viathe multiplexer of FIG. 19D. Each STP controlled boundary scan operationcycle is defined by; (1) a shifting step where data is shifted throughFF's 1905 from TDI/SI to TDO/SO, (2) an update step where the datashifted into FFs 1905 is updated into FFs 1904, and (3) a capture stepwhere Fl data is captured into FFs 1905. In this STP controlled example,shifting of data through the boundary scan register 1901 occurs on therising edge of each CK while CS is high, from a first shift to a lastshift. Following the last shift, the CS transitions low. On the fallingedge of the last shift CK, and while CS is low, the UC is generated toproduce the update step mentioned above. The STPUC signal that drivesthe UC signal is produced in response to the TMS/CS and TCK signals.FIG. 20B illustrates and example circuit for producing the STPUC signalin response to appropriate TMS/CS and TCK signal conditions. The UCsignal clocks FFs 1904 to update the data from FFs 1905 to the FOoutputs of the boundary scan register. On the next rising CK edge afterthe update step, FFs 1905 perform the capture step of loading data fromthe FI inputs of the boundary scan register. These shift update andcapture steps are indicated in the timing diagram of FIG. 20A and arerepeated during each STP controlled boundary scan cycle.

In the timing diagram, the capture step occurs one half of a CK periodafter the update step. This allows STP controlled boundary scan testoperations to be more effective at performing delay tests thanconventional TAP controlled boundary scan test operations. This improveddelay testing advantage will be described in more detail in regard toFIGS. 21 and 22.

The STP controlled timing can be used to simultaneously operate both theboundary scan cell 2010 and internal scan cell 2011 types of FIG. 20C.The advantage of being able to operate both cell types during STPcontrolled testing will be described in more detail in regard to FIG.22.

FIG. 21 illustrates an IC containing cores 1-3, each core containing aTAP/STP interface coupled to tester controlled scan path 910 and aboundary scan register 1901. In this example, the cores have been setup,as described in regard to FIG. 19A, for STP controlled boundary scantesting of connection circuits 2101-2104. Core 1 interfaces to theexternal tester via connection circuitry 2101, Cores 1 and 2 interfaceinternally via connection circuit 2102, Cores 2 and 3 interfaceinternally via connection circuit 2103, and Core3 interfaces to theexternal test connection circuit 2104. Connection circuits 2101-2104 arethe functional connections between the cores and IC input and outputpins to enable the cores to operate and produce the IC's intendedfunctionality. Connection circuits 2101-2104 contain both simpleconnections that pass signals through wires and complex connections thatpass signals through logic circuitry. Both simple and complex connectiontypes need to be tested using the STP controlled boundary scan testoperation.

The STP controlled boundary scan testing is achieved by the testercontrolling the scan path 910 to repetitively cycle the core TAP/STPinterfaces through the shift, capture, and update steps described inregard to FIG. 20A. The shift step loads stimulus data into the boundaryscan registers (BSR) 1901 from the tester and unloads capture responsedata from the BSRs 1901 to the tester. Following the shift step, theupdate step outputs the loaded stimulus data from the FO outputs of theBSRs. Following the update step, the capture step loads response datainto the BSRs from the FT inputs. During the update and capture stepsequence, test signals pass through connection circuits 2101-2104 totest both the simple and complex connection types. Connection circuits2102 and 2103 are tested by using only the BSRs 1901 of cores 1, 2, and3. Connection circuits 2101 and 2104 are tested using the externaltester and BSRs 1901 of cores 1 and 3.

Two types of STP controlled boundary scan tests may be performed, astructural test which verifies that test signals can propagate throughthe simple and complex connections, and a delay test which verifies thatthe test signals propagate through the simple and complex connectionswithin a given amount of time. The structural test may successfullypropagate the test signals through the connections, but the IC may failto operate at its rated speed due to certain ones of the connectionshaving a slow signal propagation time. Therefore, the delay test isimportant since it allows testing that the test signals can successfullypropagate through the connection within a time frame that enables the ICto operate at it rated speed. A TAP controlled boundary scan test canalso perform the structural and delay tests. A TAP controlled structuraltest is just as effective as the STP controlled structural test.However, as will described below, a TAP controlled delay test is not aseffective as the STP controlled delay test.

From the timing diagram of FIG. 20A it is seen that the STP controlledcapture step occurs on the rising CK edge following the falling CK edgethat initiates the update step. If CK is driven by the tester at a highfrequency, very effective delay testing can be achieved using STPcontrolled boundary scan testing since the delay test occurs within onehalf a CK period. TAP controlled delay testing is not as effective asSTP controlled delay testing do to the state transition mapping of theTAP controller state machine of FIG. 2. For example, the steps ofupdating data in the Update-DR state then capturing data in theCapture-DR state are separated in time by two and one half CK periods(CK is TCK). This can be seen by the rising CK edge activated statetransitions from Update-DR to Select-DR to Capture-DR to Shift-DR, andby recognizing that data is updated on the falling edge of CK during theUpdate-DR state and captured on the rising edge of CK during theCapture-DR to Shift-DR state transition. Thus a TAP controlled delaytest operates using two and a half CK periods, as opposed to the onehalf CK period used in the STP controlled delay test.

FIG. 22 illustrates an IC or core being tested via the TAP/STPinterface. In this example, the boundary scan registers (BSR) 2201-2202and internal scan registers (ISR) 2203-2204 of the IC or core have beenserially daisy-chained together between TDI/SI and TDO/SO and placed inan STP controlled test mode using a BSR&ISR scan instruction designedfor that purpose. Substituting the daisy-chained BSR and ISR scanregister of FIG. 22 for the boundary scan register 1901 of FIG. 19A, itshould be clear from the previous instruction control descriptions howthe BSR&ISR scan instruction may be loaded into the TAP's instructionregister to configure the TAP/STP interface into the configuration shownin FIG. 22.

During test, a tester coupled to the TAP/STP interface repetitivelyexecutes STP controlled scan cycles on the FIG. 22 daisy-chained BSR&ISRscan register to test the combinational logic circuits 2205-2207residing between the BSR 2201-2202 and ISR 2203-2204 scan registersections. Each scan cycle includes the shift, update, and capture stepsdescribed in the timing diagram of FIG. 20A. Conventional boundary scancells 2010 of FIG. 20C are used in the BSR and conventional internalscan cells 2011 of FIG. 20C are used in the ISR. During the shift step,scan cells 2010 and 2011 shift data from SI to SO through thedaisy-chained BSR& ISR register from TDI/SI to TDO/SO. During the shiftstep, the FO outputs of scan cells 2010 do not ripple with the SO outputbecause the update FF 2002 maintains the FO output at a constant stateduring the shift step. However, the FO output of scan cells 2011 doripple with the SO output. During the update step, the FO output of thescan cells 2010 change as the update FF 2002 is loaded by the UC controlsignal of FIG. 20A. Prior to the update step, the FO outputs of the scancells 2011 have already been established by the last shift operation ofFIG. 20A. So, from the STP controlled timing diagram of FIG. 20A, it isseen that the FO outputs of the ISR scan cells 2011 are made availableimmediately after the last shift operation, whereas the availability ofthe FO outputs of the BSR scan cells 2010 are delayed until the updatestep, which is one half CK period after the last shift operation. Duringthe capture step, the data on the Fl inputs of BSR scan cells 2010 andISR scan cell 2011 are loaded into shift FF 2001 and 2003 respectively.

The STP controlled scan test example of FIG. 22 provides a method ofallowing both conventional boundary scan cells 2010 and conventionalinternal scan cells 2011 to be daisy-chained together and operated usingthe common shift, update, and capture steps shown in the timing diagramof FIG. 20A. Traditionally, it has been necessary to access the BSRs2201-2202 separately using the TAP controller of FIG. 1A. Alsotraditionally, it has been necessary to access the ISRs 2202-2203separately using the STP controlled CS and CK signal sequencing of FIG.20A. The reason for this is because the boundary scan cells 2010 of theBSR require the update step (i.e. Update-DR state of FIG. 2) between theshift (Shift-DR state of FIG. 2) and capture (Capture-Dr state of FIG.2) steps to load data into the update FF 2002. Since internal scan cells2011 do not have an update FF to load, they only require the shift andcapture steps provided by the CS and CK signals of the STP timingdiagram of FIG. 20A. Thus the difficulty of daisy-chaining BSRs2201-2202 and ISRs 2203-2204 together as shown in FIG. 22 and operatingthe daisy-chained BSR&ISR scan register using either TAP control or STPcontrol has been how to resolve the update step situation. Some knownmethods for handling the update step in internal scan cells 2011 whenusing the TAP controller include; (1) gating off the CK input to theinternal scan cells 2011 during the update (Update-DR state) step, or(2) using a three input multiplexer in place of the two inputmultiplexer in internal scan cells 2011 and controlling the thirdmultiplexer input to feed the output of the shift FF 2003 to the inputof shift FF 2003 during the update step (Update-DR state), such that thestate of the shift FF is maintained during the update step. The drawbackof the first method is that it requires inserting gating circuitry inthe CK tree wiring, which should be avoided since clock tree routing iscritical in an IC or core. The drawback of the second method is that itadds circuitry (three input multiplexer vs two input multiplexer) toeach internal scan cell 2011, which should be avoided because itincreases test circuit overhead in the IC or core.

To overcome these conventional drawbacks of accessing scan registerswhich include mixtures of daisy-chained BSR 2201-2202 and ISR 2203-2204sections, the present disclosure provides and appropriately controls theUC signal of FIG. 20A to perform the update step required for the BSRsections of daisy-chained BSR& ISR scan registers. In FIG. 20A, the CSand CK signal timing for performing the shift and capture steps ininternal scan cells 2011 is conventional. However, the generation andpositioning of the UC signal between the last shift step and the capturestep is new and is what allows the present disclosure to easily operatescan registers which include daisy-chained BSR and ISR sections withoutincurring the previously mentioned drawbacks. The use of the UC signalis transparent to internal scan cells 2011 since they only haveconnections to CS and CK. Also, the timing of the UC signal occurs suchthat it does not effect the conventional timing of the CS and CK signalsto the internal scan cells 2011. The timing diagram of FIG. 20A not onlytransparently provides the BSR required update step, via UC, it does soin a way that supports effective delay testing of combinational logiccircuits 2205 and 2207 that reside between BSR and ISR sections of thedaisy-chained scan register of FIG. 22. This can be seen in FIG. 20A,where the BSR sections of the FIG. 22 scan register respond to the UCsignal to update their FO outputs one half a CK period prior to thecapture step that causes the scan cells 2010 and 2011 of the BSR and ISRscan register sections to load data at their Fl inputs. For the samereasons stated for the boundary scan delay test of FIG. 21, the STPcontrolled delay test of the combinational logic circuits 2205-2207 ofFIG. 22 is more effective than a TAP controlled delay test of the samecircuits 2205-2207.

FIGS. 9, 11, 13, 15, 17, 18, and 21 of the present disclosure haveillustrated the TAP/STP interfaces as always being connected to the scanpath 910. While this is one way to connect TAP/STP interfaces, thefollowing description will describe another method of providing accessto TAP/STP interfaces. The following connection approach was developedto provide selective access to one or more TAP domains existing within asystem IC. The word domain simply indicates the circuitry the TAPprovides access to, such as the circuits of FIGS. 1C-1F. In thedescription below, an overview of the TAP domain access approach will begiven, then improvements to the TAP domain access approach will bedescribed to show how it can be used to provide selective access to oneor more TAP/STP domains as well. The TAP domain selection approach isthe subject of related provisional patent application Ser. No.60/207,691 filed May 26, 2000, entitled “Improvements In or Related to1149.1 TAP Linking Modules”, which is incorporated herein by reference.

Overview of TAP Domain Access

IEEE 1149.1 TAPs may be utilized at both IC and intellectual propertycore design levels. TAPs serve as serial communication ports foraccessing a variety of embedded circuitry within ICs and coresincluding; IEEE 1149.1 boundary scan circuitry, built in test circuitry,internal scan circuitry, IEEE 1149.4 mixed signal test circuitry, IEEEP5001 in-circuit emulation circuitry, and IEEE P1532 in-systemprogramming circuitry. Selectable access to TAPs within ICs is desirablesince in many instances being able to access only the desired TAP(s)leads to improvements in the way testing, emulation, and programming maybe performed within an IC. The following describes how TAP domainsembedded within an IC may be selectively accessed using 1149.1instruction scan operations.

FIG. 23 illustrates an example arrangement for connecting multiple TAPdomains within an IC to a single scan path. Each TAP domain in FIG. 23is a complete TAP architecture like that shown and described in regardto FIG. 1A. While only one IC TAP domain 2301 exists in an IC, anynumber of core TAP domains 1-N 2302-2303 may exist within an IC. As seenin FIG. 23, the IC TAP domain and Core 1-N TAP domains are daisy-chainedbetween the IC's TDI and TDO pins. All TAP domains are connected to theIC's TMS, TCK, and TRST signals and operate according to the statediagram of FIG. 2. During instruction scan operations, instructions areshifted into each TAP domain instruction register. One drawback of theTAP domain arrangement of FIG. 3 is that it does not comply with theIEEE 1149.1 standard, since, according to the rules of that standard,only the ICs TAP domain 2301 should be present between TDI and TDO whenthe IC is initially powered up. A second drawback of the TAP domainarrangement of FIG. 23 is that it may lead to unnecessarily complexaccess for testing, in-circuit emulation, and/or in-circuit programmingfunctions associated with ones of the individual TAP domains.

For example, if scan testing is required on circuitry associated withthe Core 1 TAP domain, each of the scan frames of the test pattern setdeveloped for testing the Core 1 circuitry must be modified from theiroriginal form. The modification involves adding leading and trailing bitfields to each scan frame such that the instruction and data registersof the leading and trailing TAP domains become an integral part of thetest pattern set of Core 1. Serial patterns developed for in-circuitemulation and/or in-circuit programming of circuitry associated with theTAP domain of Core 1 must be similarly modified. To overcome these andother drawbacks of the TAP arrangement of FIG. 23, the TAP selectionarchitecture described below is provided.

FIG. 24 illustrates the preferred structure for connecting multiple TAPdomains within an IC according to provisional patent application Ser.No. 60/207,691 filed May 26, 2000, entitled “Improvements In or Relatedto 1149.1 TAP Linking Modules”. The structure includes input and outputlinking circuitry 2401 and 2402 for connecting one or more TAP domainsto the ICs TDI, TDO, TMS, TCK and TRST pins, and a TAP Linking Module(TLM) circuit 2403 for providing the control to operate the input andoutput linking circuitry.

The input linking circuitry receives as input; (1) the TDI, TMS, TCK,and TRST IC pins signals, (2) the TDO outputs from the IC TAP (ICT)domain (TDOICT), the Core 1 TAP (CIT) domain (TDOCIT), and the Core NTAP (CNT) domain (TDOCNT), and (3) TAP link control bus 2404 input fromthe TLM. The TCK and TRST inputs pass unopposed through the inputlinking circuitry to be input to each TAP domain. The TMS input to theinput linking circuitry is gated within the input linking circuitry suchthat each TAP domain receives a uniquely gated TMS output signal. Asseen in FIG. 24, the IC TAP domain receives a gated TMSICT signal, theCore 1 TAP domain receives a gated TMSCIT signal, and the Core N TAPdomain receives a gated TMSCNT signal. Example circuitry for providingthe gated TMSICT, TMSCIT, and TMSCNT signals is shown in FIG. 25. InFIG. 25, the ENAICT, ENACIT, and ENACNT signals used to gate the TMSICT,TMSCIT, and TMSCNT signals, respectively, come from the TLM via the TAPlink control bus.

From FIG. 25 it is seen that TMSCNT can be connected to TMS to enablethe Core N TAP domain or be gated low to disable the Core N TAP domain,TMSCIT can be connected to TMS to enable the Core 1 TAP domain or begated low to disable the Core 1 TAP domain, and TMSICT can be connectedto TMS to enable the IC TAP domain or be gated low to disable the IC TAPdomain. When a TAP domain TMS input (TMSCNT, TMSCIT, TMSICT) is gatedlow, the TAP domain is disabled by forcing it to enter the Run Test/Idlestate of FIG. 2. A disabled TAP domain will remain in the Run Test/Idlestate until it is again enabled by coupling it to the IC's TMS pin inputas mentioned above.

The TDI, TDOCNT, TDOCIT, and TDOICT inputs to the input linkingcircuitry are multiplexed by circuitry within the input linkingcircuitry such that each TAP domain receives a uniquely selected TDIinput signal. As seen in FIG. 24, the IC TAP domain receives a TDIICTinput signal, the Core 1 TAP domain receives a TDICIT input signal, andthe Core N TAP domain receives a TDICNT input signal. Example circuitryfor providing the TDIICT, TDICIT, and TDICNT input signals is shown inFIG. 26. In FIG. 26, the SELTDIICT, SELTDICIT, and SELTDICNT controlsignals used to select the source of the TDIICT, TDICIT, and TDICNTinput signals, respectively, come from the TLM via the TAP link controlbus. From FIG. 26 it is seen that TDICNT can be selectively connected toTDI, TDOCIT, or TDOICT, TDICIT can be selectively connected to TDI,TDOCNT, or TDOICT, and TDIICT can be selectively connected to TDI,TDOCNT, or TDOCIT.

The output linking circuitry receives as input; (1) the TDOCNT outputfrom the Core N TAP domain, the TDOCIT output from the Core 1 TAPdomain, the TDOICT output from the IC TAP domain, and TAP link controlbus 2404 input from the TLM. As seen in FIG. 24, the output linkingcircuitry outputs a selected one of the TDOCNT, TDOCIT, and TDOICT inputsignals to the TLM via the output linking circuitry TDO output. Examplecircuitry for providing the multiplexing of the TDOICT, TDOCIT, andTDOCNT signals to the TDO output is shown in FIG. 27. In FIG. 27, theSELTDO control input used to switch the TDOICT, TDOCLT, or TDOCNTsignals to TDO come from the TLM via the TAP link control bus. From FIG.27 it is seen that any one of the TDOCNT, TDOCIT, and TDOICT signals canbe selected as the input source to the TLM.

The TLM circuit receives as input the TDO output from the output linkingcircuitry and the TMS, TCK, and TRST IC input pin signals. The TLMcircuit outputs to the IC's TDO output pin. From inspection, it is seenthat the TLM lies in series with the one or more TAP domains selected bythe input and output linking circuitry.

As described above, the TLM's TAP link control bus 2404 is used tocontrol the input and output connection circuitry to form desiredconnections to one or more TAP domains so that the one of more TAPdomains may be accessed via the IC's TDI, TDO, TMS, TCK, and TRST pins.The TAP link control bus signals are output from the TLM during theUpdate-IR state of the TAP controller state diagram of FIG. 2.

FIG. 28A illustrates in detail the structure of the TLM. The TLMconsists of a TAP controller 2801, instruction register 2802,multiplexer 2803, and 3-state TDO output buffer 2804. The TAP controlleris connected to the TMS, TCK and TRST signals. The TDI input isconnected to the serial input (I) of the instruction register and to afirst input of the multiplexer. The serial output (O) of the instructionregister is connected to the second input of the multiplexer. Theparallel output of the instruction register is connected to the TAP linkcontrol bus 2404 of FIG. 24. The output of the multiplexer is connectedto the input of the 3-state buffer 2804. The output of the 3-statebuffer is connected to the IC TDO output pin. The TAP controller outputscontrol (C) to the instruction register, multiplexer, and 3-state TDOoutput buffer via bus 2805. The TAP controller responds to TMS and TCKinput as previously described in regard to FIGS. 1A and 2. Duringinstruction scan operations, the TAP controller enables the 3-state TDObuffer and shifts data through the instruction register from TDI to TDO.During data scan operations, the TAP controller enables the 3-state TDObuffer and forms a connection, via multiplexer 2803, between TDI andTDO.

FIG. 28B illustrates the instruction register 2802 in more detail. Theinstruction register consists of a shift register, TAP link decodelogic, and update register. The shift register has the serial input (I),serial output (O), control (C) inputs shown in FIG. 28A, paralleloutputs to the TAP link decode logic, and parallel inputs for loadingfixed logic 0 and 1 settings. The fixed logic 0 and 1 inputs areprovided for capturing logic 0 and 1 data bits into the first twoinstruction shift register bit positions closest to TDO, which is arequirement for IEEE 1149.1 compliant instruction shift registers. Theparallel output from the instruction register is input to TAP linkdecode logic. The parallel output from the TAP link decode logic isinput to the update register. The parallel output of the update registeris connected to the TAP link control bus 2402 to provide control inputto the input and output linking circuitry 2401 and 2402 of FIG. 24.During the Capture-IR state of FIG. 2, the shift register captures data(0 & 1) on the parallel input. During the Shift-IR state of FIG. 2, theshift register shifts data from TDI (I) to TDO (O). During the Update-IRstate of FIG. 2, the update register loads the decoded instructioncontrol input from the TAP link decode logic and outputs the decodedinstruction control onto the TAP link control bus 2404.

FIG. 29 illustrates various possible arrangements 2901-2907 of TAPdomain connections during 1149.1 instruction scan operations. Sinceduring instruction scan operations, the TLM's instruction register isphysically present and in series with the connected TAP domain(s)instruction register(s), the instruction scan frame for each arrangementwill be augmented to include the TLM's instruction register bits. It isassumed at this point that the TLM's instruction shift register of FIG.28 is 3 bits long and that the 3 bit instructions have been decoded bythe TLM's instruction register to uniquely select a different TAP domainconnection arrangement between the ICs TDI and TDO pins. For example andas indicated in FIG. 29, shifting in the following 3 bit TLMinstructions and updating them from the TLM to be input to the input andoutput linking circuitry will cause the following TAP domain connectionsto be formed.

As seen in arrangement 2901, a “000” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domainto be enabled and connected in series with the TLM between the TDI andTDO IC pins.

As seen in arrangement 2902, a “001” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domainand the Core 1 TAP Domain to be enabled and connected in series with theTLM between the TDI and TDO IC pins.

As seen in arrangement 2903, a “010” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domainand the Core N TAP Domain to be enabled and connected in series with theTLM between the TDI and TDO IC pins.

As seen in arrangement 2904, a “111” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domain,the Core 1 TAP Domain, and the Core N TAP domain to be enabled andconnected in series with the TLM between the TDI and TDO IC pins.

As seen in arrangement 2905, a “100” instruction shifted into andupdated from the TLM instruction register will cause the Core 1 TAPDomain to be enabled and connected in series with the TLM between theTDI and TDO IC pins.

As seen in arrangement 2906, a “101” instruction shifted into andupdated from the TLM instruction register will cause the Core 1 TAPDomain and Core N TAP domain to be enabled and connected in series withthe TLM between the TDI and TDO IC pins.

As seen in arrangement 2907, a “110” instruction shifted into andupdated from the TLM instruction register will cause the Core N TAPDomain to be enabled and connected in series with the TLM between theTDI and TDO IC pins.

At power up of the IC, the TLM 3-bit instruction shall be initialized to“000” to allow only the IC TAP domain arrangement 2901 to be enabled andcoupled between TDI and TDO. This complies with the IC power uprequirement established in the IEEE 1149.1 standard. Following power up,an instruction scan operation can be performed to shift instruction datathrough the IC TAP domain and the serially connected TLM to load a newIC TAP domain instruction and to load a new 3 bit instruction into theTLM. If the power up IC TAP domain arrangement 2901 is to remain ineffect between TDI and TDO, the 3 bit “000” TLM instruction of FIG. 29will be re-loaded into the TLM instruction register during the abovementioned instruction scan operation. However, if a new TAP domainarrangement is to desired between TDI and TDO, a different 3 bit TLMinstruction will be loaded into the TLM instruction register during theabove mentioned instruction register scan operation.

From the description given above, it is clear that a different TAPdomain arrangement may be selected by the TLM's instruction registerfollowing each 1149.1 instruction scan operation, more specificallyduring the Update-IR state (FIG. 2) of each instruction scan operation.Thus the TAP domain selection process comprises only the single step ofperforming an instruction scan operation to load instructions into theinstruction registers of the currently selected TAP domains and TLM.

The following briefly re-visits and summarizes the operation of the TLMand input and output linking circuitry to clarify the TAP domainarrangement switching illustrated in FIG. 29. As previously described inregard to FIG. 24, the TMS inputs of enabled TAP domains are coupled tothe IC's TMS input pin (via the gating circuitry of FIG. 25), while theTMS inputs of disabled TAP domains are gated to a logic low (via thegating circuitry of FIG. 25). Also, enabled TAP domains are seriallyconnected (via the multiplexers of FIGS. 26 and 27) to form the desiredserial TAP domain connection between the IC's TDI and TDO pins, theconnection including the TLM. All the control for enabling or disablingthe TAP domain TMS inputs and for forming serial TAP domain connectionsbetween the IC's TDI and TDO pins comes from the TLM's TAP link controlbus. The control output from the TAP link control bus changes stateduring the Update-IR state of the TAP state diagram of FIG. 2. So, allTAP domain connection arrangement changes take place during theUpdate-IR state.

FIG. 30 is provided to illustrate that during 1149.1 data scanoperations the TLM 2403 is configured, as described in regard to FIG.28, to simply form a connection path between the output of the selectedTAP domain arrangement 3001-3007 and the IC's TDO pin. Thus the TLM 2403does not add bits to 1149.1 data scan operations as it does for 1149.1instruction scan operations. TAP domain arrangements 3001-3007 for1149.1 data scans are the same as TAP domain arrangements 2901-2907 for1149.1 instruction scans, with the exception that during data scans theoutput of the selected TAP domain arrangement 3001-3007 passes directlythrough the TLM to TDO, as opposed to passing through the TLM'sinstruction register during instruction scans to TAP domain arrangements2901-2907.

FIG. 31 illustrates how the structure of the TLM architecture of FIG. 24may be adapted to support TAP/STP domains instead of TAP domains. FromFIG. 31 it is seen that the basic structure of the TLM architecture ofFIG. 24 is maintained when using TAP/STP domains in place of TAPdomains. The changes seen in FIG. 31 involve renaming TDI to TDI/SI, TDOto TDO/SO, TMS to TMS/CS, TDICNT to TDI/SICNT, TDICIT to TDI/SICIT,TDIICT to TDI/SIICT, TMSCNT to TMS/CSCNT, TMSCIT to TMS/CSCIT, TMSICT toTMS/CSICT, TDOCNT to TDO/SOCNT, TDOCIT to TDO/SOCIT, and TDOICT toTDO/SOICT, to represent the different signal types used by the TAP/STPdomains. The name of the TAP link control bus of FIG. 24 has also beenchanged to TAP/STP link control bus 3104 in FIG. 31.

FIGS. 32 and 33 represent the TAP/STP domain signal name substitutionfor the TAP domain signal names in the TMS gating circuitry and TDImultiplexing circuitry of the input circuitry 3101 of FIG. 31. Thecontrol inputs to the TDI/SI multiplexer circuitry of FIG. 33, from theTAP/STP link control bus of FIG. 31, are also changed from SELTDICNT toSELTDI/SICNT, SELTDICIT to SELTDI/SICIT, and SELTDIICT to SELTDI/SIICT.FIG. 34 represents the TAP/STP domain signal name substitution for theTAP domain signal names of the output circuitry 3102 of FIG. 31. Thegating and multiplexing circuitry of FIGS. 32-34 respond to TLM 3103instruction control output on TAP/STP control bus 3104 as previouslymentioned. The only circuit changes between the TLM architecture ofFIGS. 24 and 31, excluding the substitution of TAP/STP domains for TAPdomains and the signal renaming mentioned above lies within TLM 3103 asdescribe below.

It should be clear that the TMS/CSCNT, TMS/CSCIT, TMS/CSICT outputs ofthe AND gates in FIG. 32 are each input to a respective AND gate 503(FIG. 7) of the Core N, Core 1, and IC TAP/STP interfaces of FIG. 31.From this, it should clear that a three input AND gate 503 (FIG. 7)could be substituted for the two input AND gate 503 to allow the thirdinput to directly input the ENACNT, ENACIT, and ENAICT signals from theTLM 3103. This would eliminate the need for the AND gates of FIG. 32 andreduce the signal propagation delay of the TMS/CS input to the TAPcontroller of the TAP/STP interfaces.

FIG. 35A illustrates a detail view of TLM 3103 of FIG. 31. Like TLM 2403of FIG. 28, TLM 3103 contains a TAP controller 3501, instructionregister 3502, multiplexer 3503, and 3-state buffer 3504. Unlike TLM2403, TLM 3103 additionally contains logic gates 3505, 3506, 3507, and aTAP lock circuit 3508. The TAP controller outputs the Update-IR signal3509 to TAP lock circuit 3508, as described in regard to FIG. 7. Theinstruction register 3502 outputs the Lock in signal 3510 to the TAPlock circuit, as described in FIG. 7. The TAP lock circuit outputs theLock out signal 3511 from the TLM and to gates 3505, 3506, and 3507.Gate 3507 serves the same function as gate 503 of FIG. 7, that beinggating the TMS input to the TAP controller 3501 on when Lock out is highand off when Lock out is low. When Lock out is high (TAP unlocked),gates 3505 and 3506 pass signals from the TAP controller bus 3512 tooperate multiplexer 3503 and 3-state buffer 3504, during TAP controllerinstruction and data scan operations as previously described with TLM2403 of FIG. 28. When Lock out is low (TAP is Locked), the output ofgate 3505 is set, via the Lock out signal, to select the TDI/SI input tomultiplexer 3503 to be input to buffer 3504. Also while Lock out is low,the output of gate 3506 is set, via the Lock out signal, to enable theoutput of buffer 3504 to drive TDO/SO.

The TAP lock process of; (1) inputting an instruction into theinstruction register of TLM 3103 to set the Lock in signal 3510 high,(2) clocking the Lock in signal into the TAP lock circuit 3508 to setthe Lock out signal 3511 low, and (3) disabling the TAP controller 3501and enabling the TAP Lock circuit 3508 in response to the Lock outsignal going low, is the same as described previously in regard to FIGS.7, 8A and 8B. While the TAP controller 3501 is locked and the TAP Lockcircuit 3508 is enabled, STP control of TMS/CS can occur as described inregard to FIGS. 7, 8A, and 8B without unlocking the TAP controller 3501and without disabling the TAP Lock circuit 3508. The process ofunlocking the TAP controller 3501 and disabling the TAP Lock circuit3508 by setting the TMS/CS input to the TAP Lock circuit 3508 low for arequired number of TCK inputs is also the same as previously describedin regard to the TAP lock circuit descriptions of FIGS. 8A and 8B.

FIG. 35B illustrates in detail the changes required to instructionregister 3502 to enable TLM 3103 to operate in a first mode to selectand access TAP/STP domains using TAP control, or operate in a secondmode to select and access TAP/STP domains using STP control. Instructionregister 3502 is similar in structure and operation to instructionregister 2802 in that it has a shift register, a TAP/STP link decodelogic, and an update register. The differences between instructionregisters 3502 and 2802 include; (1) the shift register of 3502 is 4bits long instead of 3 bits in 2802, (2) the TAP/STP link decode logicof 3502 is designed to decode the 4 bit instruction instead of the 3 bitinstruction of 2802, and (3) the update register of 3502 includes, inaddition to the TAP/STP link control bus 3104, an output for the Lock insignal 3510.

FIG. 36 illustrates various possible arrangements 3601-3607 of TAP/STPdomain connections during 1149.1 TAP instruction scan operations usingthe TAP/STP architecture of FIG. 31. Since during instruction scanoperations, the TLM's 3103 instruction register is physically presentand in series with the connected TAP/STP domain(s) instructionregister(s), the instruction scan frame for each arrangement will beaugmented to include the TLM's 3103 4 instruction register bits. Aspreviously mentioned, the TLM's 3103 instruction shift register of FIG.35B is 4 bits long and the 4 bit instructions have been decoded by theTLM's 3103 instruction register to uniquely select a different TAP/STPdomain connection arrangement between the ICs TDI/SI and TDO/SO pins.For example and as indicated in FIG. 36, shifting in the following 4 bitTLM instructions and updating them from TLM 3103 to the input and outputlinking circuitry 3101 and 3102 will cause the following TAP/STP domainconnections to be formed.

As seen in arrangement 3601, a “0000” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP/STPdomain to be enabled and connected in series with the TLM between theTDI/SI and TDO/SO IC pins.

As seen in arrangement 3602, a “0001” instruction shifted into andupdated from the TLM instruction register will cause the IC and Core 1TAP/STP domains to be enabled and connected in series with the TLMbetween the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3603, a “0010” instruction shifted into andupdated from the TLM instruction register will cause the IC and Core NTAP/STP domains to be enabled and connected in series with the TLMbetween the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3604, a “0011” instruction shifted into andupdated from the TLM instruction register will cause the IC, Core 1, andCore N TAP/STP domains to be enabled and connected in series with theTLM between the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3605, a “0100” instruction shifted into andupdated from the TLM instruction register will cause the Core 1 TAP/STPdomain to be enabled and connected in series with the TLM between theTDI/SI and TDO/SO IC pins.

As seen in arrangement 3606, a “0101” instruction shifted into andupdated from the TLM instruction register will cause the Core 1 and CoreN TAP/STP domains to be enabled and connected in series with the TLMbetween the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3607, a “0110” instruction shifted into andupdated from the TLM instruction register will cause the Core N TAP/STPdomain to be enabled and connected in series with the TLM between theTDI/SI and TDO/SO IC pins.

At power up of the IC, the TLM 3103 4-bit instruction is initialized to“0000” to allow only the IC TAP/STP domain arrangement 3601 to beenabled and coupled between TDI/SI and TDO/SO, to comply with the EEE1149.1 standard. Following power up, an instruction scan operation canbe performed to shift instruction data through the IC TAP domain and theserially connected TLM 3103 to load a new IC TAP/STP domain instructionand to load a new 4 bit instruction into the TLM.

From the description given above, it is clear that a different TAP/STPdomain arrangement may be selected by the TLM 3103 instruction registerfollowing each 1149.1 instruction scan operation, more specificallyduring the Update-IR state (FIG. 2) of each instruction scan operation.Thus the TAP/STP domain selection process comprises only the single stepof performing an instruction scan operation to load instructions intothe instruction registers of the currently selected TAP/STP domains andTLM 3103.

FIG. 37 is provided to illustrate that during 1149.1 data scanoperations the TLM 3103 is configured, as described in regard to FIG.35A, to simply form a connection path between the output of the selectedTAP/STP domain arrangement 3701-3707 and the IC's TDO/SO pin. Thus theTLM 3103 does not add bits to 1149.1 data scan operations as it does for1149.1 instruction scan operations. TAP/STP domain arrangements3701-3707 for 1149.1 data scans are the same as TAP/STP domainarrangements 3601-3607 for 1149.1 instruction scans, with the exceptionthat during data scans the output of the selected TAP/STP domainarrangement 3701-3707 passes directly through the TLM to TDO/SO, asopposed to passing through the TLM's instruction register duringinstruction scans to TAP/STP domain arrangements 3001-3007.

Comparing the operation of the TAP controlled instruction and data scanoperations of FIGS. 36 and 37 to the TAP controlled instruction and datascan operations of FIGS. 29 and 30, it is clear that the TLMarchitectures of FIG. 31 (using TAP/STP domains) and FIG. 24 (using TAPdomains) are similar. This is because in both TLM architectures of FIGS.31 and 24, the selected TAP or TAP/STP domains are receptive to beingaccessed using IEEE 1149.1 TAP controlled instruction (FIGS. 36 and 29)and data (FIGS. 37 and 30) scan operations.

The process of selecting a TAP/STP domain arrangement of FIG. 31,placing the selected TAP/STP domain arrangement in the STP controlledmode, and accessing the selected TAP/STP domain arrangement using STPcontrol is as follows. This process example will start in TAP/STP domainarrangement 3601 of FIG. 36, then switch to TAP/STP domain arrangement3604 of FIG. 36, then switch the TAP/STP interfaces of the TAP/STPdomain arrangement 3604 from TAP control to STP control.

A first TAP controlled instruction scan is performed on TAP/STP domainarrangement 3601 to load instructions into the IC TAP/STP domain and theTLM 3103. The instruction loaded into the TLM is “0011” and theinstruction loaded into the IC TAP/STP is say an IEEE 1149.1 standardbypass instruction, a well known 1149.1 instruction. In response to the“0011” TLM instruction, the TLM architecture of FIG. 31 switches fromselecting the TAP/STP domain arrangement 3601 between TDI/SI and TDO/SOto selecting TAP/STP domain arrangement 3604 between TDI/SI and TDO/SO,as previously described. A second TAP controlled instruction scan isperformed through the IC, Core 1, and Core N TAP/STP domains and TLM ofarrangement 3604. This second instruction scan loads an STP controlledtest instruction, like the previously described STP controlled scan testinstruction of FIGS. 5-9, into the IC, Core 1, and Core N TAP/STPinterfaces and also loads the TLM with a “1011” instruction which willbring about the STP controlled TAP/STP domain arrangement 3804 seen inFIG. 38. In response to the second instruction scan, the IC, Core 1, andCore N TAP/STP interfaces switch from TAP control to STP control forperforming the STP controlled the scan test instructions, as describedin regard to the daisy-chained cores 1-N of FIG. 9. Also in response tothe second instruction scan, the “1011” instruction loaded into the TLM3103 instruction register causes the TLM to switched from TAP control toSTP control.

The switching of the TLM 3103 from TAP to STP control can best beunderstood by inspection of FIGS. 35A and 35B. When the “1011”instruction is updated from the TLM instruction register, the Lock inoutput 3510 from the TLM instruction register goes high. The high onLock in 3510 is input to TAP lock circuit 3508. In response to the highon Lock in 3510 and when the TAP lock circuit 3508 receives theUpdate-IR clock 3509 from TAP controller 3501, the TAP lock circuit isenabled and drives its Lock out signal 3511 low. The low on Lock out3511 disables TAP controller 3501, forms a connection from TDI/SIthrough multiplexer 3503 to the input of 3-state buffer 3504, andenables the output of 3-state buffer 3504 to drive out on TDO/SO, aspreviously described using gates 3505-3507. Once placed in the STPcontrolled mode, TLM 3103 will remain in the STP controlled mode untilthe previously described TMS/CS escape sequence is input to the TAP lockcircuit's unlock state machine as described in regard to FIGS. 8A and8B.

While in the STP controlled TAP/STP domain arrangement 3804, scantesting of IC, Core 1 and Core N occurs as described previously inregard to the cores 1-N of FIG. 9. In the TAP/STP domain arrangement3804, as in the TAP domain arrangement 3704, the TLM 3103 does not addbits to the scan patterns shifted through the IC, Core 1 and Core Nduring the STP controlled scan test operations. At the end of the STPcontrolled scan test operation to TAP/STP domain arrangement 3804, theTMS/CS is set low to cause the IC, Core 1, Core 2, and TLM to switchfrom the STP controlled mode to the TAP controlled mode, as previouslydescribed in FIGS. 8A and 8 b.

After the TAP/STP domain arrangement 3804 returns to the TAP controlledmode, a TAP controlled instruction scan, as described in regard toTAP/STP domain arrangement 3604 is executed to load differentinstructions into the IC, Core 1, Core N and TLM instruction register.The loaded instructions may select another TAP/STP domain arrangementfor testing using either TAP or STP control. In a first example, and inresponse to the above mentioned TAP controlled instruction scanoperation, if the TLM's instruction register were loaded with a “1110”instruction and Core N were loaded with a different type of STPcontrolled test instruction, the Core N TAP/STP domain arrangement 3807would be selected between TDI/SI and TDO/SO for testing Core N via STPcontrol of the different test instruction. In a second example, and inresponse to the above mentioned TAP controlled instruction scanoperation, if the TLM's instruction register were loaded with a “0100”instruction and Core 1 were loaded with a different type of TAPcontrolled test instruction, the Core 1 TAP/STP domain arrangement 3605would be selected between TDI/SI and TDO/SO for testing Core 1 via TAPcontrol of the different test instruction. In general, any TAP/STPdomain arrangement can be selected by the above mentioned TAPinstruction scan operation to load instructions into a currentlyselected TAP/STP domain arrangement and TLM to select a new TAP/STPdomain arrangement and initiate either TAP or STP controlled testing onthe new TAP/STP domain arrangement.

Instructions not related to testing but rather to other embeddedfunctions, such as the in-circuit emulation or in-circuit programmingexamples of FIGS. 1D and 1E, may be loaded into particular TAP/STPdomain arrangements along with a TLM instruction for selecting theparticular TAP/STP domain arrangement to allow the other embeddedfunctions to be operated from either TAP or STP control. Furthermore,any type of instruction may be loaded into a TAP/STP domain and executedusing TAP or STP control with or without the TLM. For example, a fixedTAP/STP domain arrangement as shown in FIG. 9 could execute test,in-circuit emulation, or in-circuit programming instructions usingeither TAP or STP control.

In FIG. 39, a dotted line connection 3901 is shown formed between TLM3103 and IC, Core 1, and Core N TAP/STP domains. This is provided toillustrate another example implementation of the present disclosurewhereby the externally available Lock out signal 3511 of the TLM's TAPlock circuit 3508 is used to provide the Lock Out signal to the TAP/STPdomains which, in this example, do not themselves have TAP lockcircuits. In this example, the TAP/STP domain interfaces are equippedwith input terminals 3902-3904 for inputting the Lock Out signal 3511from TLM 3103 via connection 3901. The TAP/STP domain interfaces of FIG.39 utilize the FIG. 6 TAP/STP interface style which does not include theTAP lock circuit, but rather inputs the Lock Out signal via an inputterminal. The operation of this alternate realization of the presentdisclosure to switch between TAP and STP controlled modes is the same aspreviously described. The use of the TLM's TAP lock circuit 3508 togenerate the Lock out signal to a plurality of TAP/STP domain interfaceswhich themselves don't have TAP lock circuits, as shown in FIG. 39,should be understood to be an alternate method of implementing thepresent disclosure in all TLM examples described herein. In someimplementations, the use of the TLM's TAP lock circuit 3508 to generatethe Lock out signal to other TAP/STP domain interfaces as shown in FIG.39 may be preferred since it eliminates the need for each TAP/STP domaininterface to have its own TAP lock circuit.

FIG. 40 illustrates another advantage of the TLM architecture. Today,many legacy, or pre-existing, cores exist that use the conventional TAPinterface of FIG. 1A. These cores do not comprehend or anticipate use ofSTP control as an alternate method of using the TAP interface to accessembedded functions such as boundary scan, internal scan, in-circuitemulation/debug, or in-circuit programming. In FIG. 40, an IC TAP/STPdomain, Core 1 TAP domain, and Core N TAP/STP domain are shown withinthe TLM architecture of FIG. 31. The IC TAP/STP, Core 1 TAP, and Core NTAP/STP domains are all accessible during TAP controlled operations. Forexample, in FIG. 41 all combinations of TAP/STP and TAP domainsarrangements 4101-4107 are shown being accessible between TDI/SI andTDO/SO during TAP controlled instruction scan operations, as previouslydescribed in regard to FIGS. 29 and 36. Also in FIG. 42, allcombinations of TAP/STP and TAP domain arrangements 4201-4207 are shownbeing accessible between TDI/SI and TDO/SO during TAP controlled datascan operations, as previously described in regard to FIGS. 30 and 37.However, in FIG. 43 it is seen that only the TAP/STP domainsarrangements 4301, 4303, and 4307 can be connected between TDI/SI andTDO/SO and accessed using STP control. Connecting the Core 1 TAP domaininto the STP controlled arrangements of 4302, 4304, 4305, and 4306 wouldnot work since the TAP interface of Core 1 would not be able to shift,update, and capture with the STP control applied on TMS/CS. For example,if the TAP interface of Core 1 were included in arrangements 4302, 4304,4305, and/or 4306, it would attempt to interpret the STP's shift,update, and capture control on TMS/CS to transition through the TAPcontroller state diagram of FIG. 2. This would clearly corrupt anddisable the STP controlled shift, update, and capture operations to theTAP/STP interface(s) within the 4302, 4304, 4305, and/or 4306arrangements. Thus the TLM architecture of FIG. 31 advantageously servesto selectively partition conventional legacy TAP interfaces from TAP/STPinterfaces during STP controlled access.

It should be understood that while FIGS. 9, 11, 15, 17, 18, 21, 23, 24,31, 39, and 40 and accompanying descriptions have depicted the presentdisclosure as it would be applied and used to select core TAP/STPdomains within an IC, the present disclosure can also be similarlyapplied and used to select sub-circuit TAP/STP domains within individualcores as well. For example, FIG. 9 could depict sub-circuits 1-N in acore, each sub-circuit having a TAP/STP interface connected to a corelevel scan path 910. FIG. 31 could depict sub-circuits in a core, eachsub-circuit having a TAP/STP interface connected to input and outputcircuitry 3101, 3102 and TLM circuit 3103 in the core. FIG. 40 coulddepict sub-circuits in a core, some sub-circuits having TAP/STPinterfaces and some having TAP interfaces and all connected to input andoutput circuitry 3101, 3102 and TLM circuit 3103 in the core.

Furthermore, it should again be understood that while FIGS. 9, 11, 15,17, 18, 21, 23, 24, 31, 39, and 40 and accompanying descriptions havedepicted the present disclosure as it would be applied and used toselect core TAP/STP domains within an IC, the present disclosure canalso be similarly applied and used to select IC TAP/STP domains on amulti-chip module, a board, or a higher level circuit block, such as asystem backplane. For example, FIG. 9 could depict ICs 1-N on a board,each IC having a TAP/STP interface connected to a board level scan path910. FIG. 31 could depict ICs on a board, each IC having a TAP/STPinterface connected to input and output circuitry 3101, 3102 and TLMcircuit 3103 on the board. FIG. 40 could depict ICs on a board, some ICshaving TAP/STP interfaces and some having TAP interfaces and allconnected to input and output circuitry 3101, 3102 and TLM circuit 3103on the board.

Additionally, while the present disclosure has shown the use of a dualmode test access port wherein the first mode is TAP controlled and thesecond mode is STP controlled, the dual mode port concept is general andcan be applied to other type of first and second mode controls as well.For example, a dual mode test access port may be implemented wherein theTAP control is used for the first mode and a control different from theSTP control is used for the second mode. This alternate second modecontrol was implied earlier in regard to the alternate STP “back toback” capture control operation description of FIG. 8B.

1. An integrated circuit comprising: A. a substrate carrying a serialdata input lead, a serial data output lead, a select lead, and a clocklead; B. functional circuitry on the substrate having data input leadsand data output leads; C. test access port circuitry on the substratehaving: i. a test data input lead connected to the serial data inputlead, ii. a test data output lead connected to the serial data outputlead, iii. a TAP controller having a test mode select input leadselectively coupled to the select lead, a test clock input leadconnected to the clock lead, data register control leads, instructionregister control leads, a multiplexer select output lead, and a bufferenable output lead, iv. a data register having a data input connected tothe test data input lead and having a data output, v. an instructionregister having a data input connected to the test data input, a dataoutput, and scan circuitry control output leads, vi. a multiplexerhaving a first input connected to the data output of the data register,a second input connected to the data output of the instruction register,a control input connected with the multiplexer select output lead, and adata output, and vii. an output data buffer having an input coupled tothe data output of the multiplexer, a control input connected with thebuffer enable output lead, and an output connected to the test dataoutput lead; D. scan test port circuitry on the substrate having: i. ascan input lead connected to the serial data input lead, ii. a scanoutput lead selectively coupled to the serial data output lead, iii. acapture select input lead, iv. a scan clock input lead, and v. a scanregister connected between the scan input lead and the scan output lead,the scan register having functional data output and input leadsconnected to the functional circuitry data input leads and data outputleads; E. connection circuitry on the substrate coupling the scan testport circuitry to the test access port circuitry, the connectioncircuitry having control inputs connected to the scan circuitry controloutput leads, the select lead, and the clock lead, and the connectioncircuitry having control outputs connected to the capture select inputlead, and the scan clock input lead; and F. a lead connected between thescan output lead and the first input of the multiplexer.
 2. Theintegrated circuit of claim 1 including a logic gate having one inputconnected to the select lead, another input connected to a lock outsignal, and an output connected to the test mode select lead.
 3. Theintegrated circuit of claim 2 including tap lock circuitry having a lockout signal output connected to the lock out signal input of the logicgate, the tap lock circuitry having inputs connected to the test accessport circuitry, the select lead, and the clock lead.
 4. The integratedcircuit of claim 3 in which the tap lock circuitry has an inputconnected to an UPDATE-IR signal from the test access port circuitry. 5.The integrated circuit of claim 2 in which the tap lock circuitryincludes a state machine having a data input connected to the selectlead.